In the field of LED lamps for general-purpose lighting, spreading and shining of light are demanded to follow (retrofit) those of incandescent light bulbs. Specifically, there is a strong demand for spreading light over a wide range from a point light source positioned in a center part of a glass globe, as in a clear electric light bulb.
However, LEDs have strong directivity, and a light distribution angle of an LED lamp is therefore as narrow as approximately 120 degrees if LEDs are used directly as a light source.
Hence, an LED lamp is commonly known which scatters light emitted from an LED over a wide range by using a light guide column. A conventional light guide column is arranged coaxially along an optical axis of an LED.
The light guide column comprises an incident plane and a tip end positioned on a side opposite to the incident plane. A scattering member is provided at the tip end of the light guide column.
When light emitted from LEDs is made to enter the incident plane of the light guide column, the incident light is led to the scattering member through the inside of the light guide column and penetrates the scattering member while the incident light is simultaneously reflected on the scattering member. Thus, the light which has penetrated and been scattered by the light guide column is emitted and diffused from the tip end of the light guide column.
A distribution angle of an LED lamp using a light guide column as described above increases as the number of times light is scattered by a scattering member increases.
However, when a scattering member is used, a part of scattered light returns in a direction of a light emitting module through a light guide column, and is absorbed by the light emitting module. In a common scattering member, internal scattering particles slightly absorb light. Therefore, when scattering takes place a greater number of times, light is absorbed at a greater ratio by a light emitting module and the scattering member.
As a result, light spreads in an improved manner while luminaire efficiency of a whole LED lamp deteriorates. There thus is still margin for improvement to effectively use the light emitted from LEDs.
Accordingly, development of a lighting apparatus is demanded which can achieve a wide light distribution and can simultaneously improve the luminaire efficiency.